There are “some links” between the deadly Easter bombings and Islamic State (IS, formerly ISIS), Sri Lanka’s prime minister has said, warning that new attacks are possible.

The country’s authorities are monitoring Islamic State recruits who have returned to the country, PM Ranil Wickremesinghe said on Tuesday.

So far, only Sri Lankan citizens have been arrested in connection with the attacks, the PM said. However, some of the suspected bombers had traveled abroad and returned home before carrying out the massacre.

The bombings of Christian churches and luxury hotels, which killed over 300 people, might have been in retaliation to the Christchurch mosque shooting in New Zealand, the official added. A fourth hotel was also a terrorist target, yet the attack failed, according to the PM.

Shortly before Wickremasinghe held the press conference, IS claimed responsibility for the attacks through its propaganda mouthpiece Amaq. While the group did not provide any evidence to back up the claims, Sri Lankan authorities are taking the statement seriously.

“We will be following up on IS claims, we believe there may be links,” Wickremasinghe stated.

Wickremasinghe revealed that the country’s intelligence units received information about the bombing plot beforehand and that a specific tip-off came from India. The investigation into the blasts is receiving international support as well. The FBI revealed that it is assisting Sri Lankan authorities.